The above exhaustive side-by-side tumor studies in two PSA− and two PSA+ tumor systems (summarized in Supplementary Table 4) demonstrate that tumor-initiating Du145 cells can be enriched by all three surface markers (ABCG2, α2β1, and CD44) as well as Aldefluor assay but not SP analysis as this model lacks the SP. Here, ABCG2 is linked to neoplasm.